Topic 8.2.2 Regulation of transcription and translation

Question 1

What are transcription factors?

Answer 1

● Proteins which regulate (stimulate or inhibit) transcription of specific target genes in eukaryotes
● By binding to a specific DNA base sequence on a promoter region

Question 2

Describe how transcription can be regulated using transcription factors

Answer 2

1. Transcription factors move from cytoplasm to nucleus
2. Bind to DNA at a specific DNA base sequence on a promoter region (before / upstream of target gene)
3. This stimulates or inhibits transcription (production of mRNA) of target gene(s) by helping or
   preventing RNA polymerase binding

Question 3

Explain how oestrogen affects transcription

Answer 3

1. Oestrogen is a lipid-soluble steroid hormone so diffuses into
   cell across the phospholipid bilayer
2. In cytoplasm, oestrogen binds to its receptor, an inactive
   transcription factor, forming an oestrogen-receptor complex
3. This changes the shape of the inactive transcription factor,
   forming an active transcription factor
4. The complex diffuses from cytoplasm into the nucleus
5. Then binds to a specific DNA base sequence on the promoter
   region of a target gene
6. Stimulating transcription of target genes forming mRNA by
   helping RNA polymerase to bind

Question 4

Explain why oestrogen only affects target cells

Answer 4

Other cells do not have oestrogen receptors

Question 5

Describe what is meant by epigenetics

Answer 5

● Heritable changes in gene function / expression without changes to the base sequence of DNA
● Caused by changes in the environment (eg. diet, stress, toxins)

Question 6

Describe what is meant by epigenome

Answer 6

All chemical modification of DNA and histone proteins - methyl groups on DNA and acetyl groups on histones

Question 7

Summarise the epigenetic control of gene expression in eukaryotes

Answer 7

check email

Question 8

Explain how methylation and acetylation can inhibit transcription

Answer 8

check email

Question 9

Explain the relevance of epigenetics on disease development and treatment

Answer 9

● Environmental factors (eg. diet, stress, toxins) can lead to epigenetic changes
● These can stimulate / inhibit expression of certain genes that can lead to disease development
○ Increased methylation of DNA OR decreased acetylation of histones inhibits transcription
○ Decreased methylation of DNA OR increased acetylation of histones stimulates transcription
● Diagnostic tests can be developed that detect these epigenetic changes before symptoms present
● Drugs can be developed to reverse these epigenetic changes

Question 10

What is RNA interference (RNAi)?

Answer 10

● Inhibition of translation of mRNA produced from target genes, by RNA molecules eg. siRNA, miRNA
● This inhibits expression of (silencing) a target gene

Question 11

Describe the regulation of translation by RNA interference

Answer 11

1. Small interfering RNA (siRNA) or micro-RNA (miRNA) is incorporated into
   / binds to a protein, forming an RNA-induced silencing complex (RISC)
   ○ siRNA synthesised as double-stranded RNA → 1 strand incorporated
   ○ miRNA synthesised as a double-stranded hairpin bend of RNA →
   both strands incorporated
2. Single-stranded miRNA / siRNA within RISC binds to target mRNA with a
   complementary base sequence
3. This leads to hydrolysis of mRNA into fragments which are then
   degraded OR prevents ribosomes binding
4. Reducing / preventing translation of target mRNA into protein